gcb12602-sup-0001-FigS1.tifimage/tif229KFigure S1. Schematic diagram showing the spatial distribution of geothermal soil warming at the FORHOT grassland sites in Reykir, Iceland (see Box 1). Isolines show differences in soil temperature (°C) at 10 cm depth between unaffected and warmed areas. (a) Grassland site which has only been exposed to geothermal warming since an earthquake in 2008; (b) Grassland site that has been geothermally heated for a much longer time period.
gcb12602-sup-0002-FigS2.tifimage/tif22102KFigure S2. (a) Heat exchangers used in the geothermal Hengill region of Iceland. The left panel shows a large heat exchanger (13 m2 surface area) used for the whole-stream warming experiment described in Box 2. This system successfully warmed a 35 m reach of the experimental stream to ~3.5 °C above ambient. The panels on the right show smaller heat exchangers used in the streamside channel experiments described in Box 2. (b) Experimental stream warming array and resulting temperature data across treatments. The channel array on the left provides a platform for replicated studies conducted along a temperature gradient at small temporal and spatial scales. A system of three small heat exchangers, shown in (a), warms water from a cool source to four controlled, higher temperatures (up to a maximum of ~25 °C), allowing three replicated experimental channels at each of five temperatures. The figure on the right shows average temperatures and box plot quantiles for an 8 week experiment in summer 2013.

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